Fast pyrolysis is a process during which organic carbonaceous biomass feedstock, i.e., “biomass”, such as wood waste, agricultural waste, algae, etc., is rapidly heated to between about 300° C. to about 900° C. in the absence of air using a pyrolysis reactor. Under these conditions, solid products, liquid products, and gaseous pyrolysis products are produced. A condensable portion (vapors) of the gaseous pyrolysis products is condensed into biomass-derived pyrolysis oil (commonly referred to as “pyoil”). Biomass-derived pyrolysis oil can be burned directly as fuel for certain boiler and furnace applications, and can also serve as a potential feedstock in catalytic processes for the production of fuels in petroleum refineries. Biomass-derived pyrolysis oil has the potential to replace up to 60% of transportation fuels, thereby reducing the dependency on conventional petroleum and reducing its environmental impact.
However, biomass-derived pyrolysis oil is a complex, highly oxygenated organic liquid having properties that currently limit its utilization as a biofuel. For example, biomass-derived pyrolysis oil has high acidity and a low energy density attributable in large part to oxygenated hydrocarbons in the oil, which can undergo secondary reactions during storage particularly if the oil is stored at elevated temperatures. “Oxygenated hydrocarbons” or “oxygenates” as used herein are organic compounds containing hydrogen, carbon, and oxygen. Such oxygenated hydrocarbons in the biomass-derived pyrolysis oil include carboxylic acids, phenols, cresols, alcohols, aldehydes, etc. Conventional biomass-derived pyrolysis oil comprises about 30% or greater by weight oxygen from these oxygenated hydrocarbons. Conversion of biomass-derived pyrolysis oil into biofuels and chemicals requires full or partial deoxygenation of the biomass-derived pyrolysis oil. Such deoxygenation may proceed via two main routes, namely the elimination of either water or CO2. Unfortunately, deoxygenating biomass-derived pyrolysis oil leads to rapid plugging or fouling of the processing catalyst in a hydroprocessing reactor caused by the formation of solids from the biomass-derived pyrolysis oil. Components in the pyrolysis oil form on the processing catalysts causing catalytic bed fouling, reducing activity of the catalyst, and causing build up in the hydroprocessing reactor. It is believed that this plugging is due to an acid catalyzed polymerization of the various components of the biomass-derived pyrolysis oil, e.g., second order reactions in which the various components of the oil polymerize with themselves, that create either a glassy brown polymer or powdery brown char that limits run duration and processibility of the biomass-derived pyrolysis oil.
Accordingly, it is desirable to provide methods for producing a low-oxygen biomass-derived pyrolysis oil without plugging of the catalyst, thereby increasing run duration and improving processibility of the biomass-derived pyrolysis oil. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.